radosgw-admin-rest: Add unit tests of radosgw-admin RESTful functionality.

Duplicate the radosgw-admin unit tests but perform them through the {admin}
RESTful endpoint.

Signed-off-by: caleb miles <caleb.miles@inktank.com>
radosgw-rest-admin: Bug fixes.

Signed-off-by caleb miles <caleb.miles@inktank.com>